Belt retractor with force-limiting arrangement

ABSTRACT

A belt retractor has a belt spool ( 12 ) rotatably mounted in a frame ( 10 ), a disc adapted to be blocked against rotation on the frame ( 10 ), and a force-limiting arrangement. The force-limiting arrangement includes a cutting body ( 22 ) which is adapted to be guided into a coupling position in which the cutting body ( 22 ) couples the belt spool ( 12 ) to the disc ( 16 ) such that upon a relative rotation between the disc ( 16 ) and the belt spool ( 12 ), the cutting body ( 22 ) cuts material. The force-limiting arrangement has a guiding-in mechanism which guides the cutting body ( 22 ) into the coupling position as a function of accident-related data.

TECHNICAL FIELD

The invention relates to a belt retractor, in particular to a belt retractor comprising a force-limiting arrangement.

BACKGROUND OF THE INVENTION

From DE-A-103 43 534 a belt retractor is known comprising a belt spool rotatably mounted in a frame, a disc adapted to be blocked against rotation on the frame, and a force-limiting arrangement with a cutting body which is adapted to be guided into a coupling position in which the cutting body couples the belt spool to the disc such that upon a relative rotation between the disc and the belt spool, the cutting body cuts material. In this belt retractor, in addition to a first force limitation by means of a torsion rod, at the same time a second force limitation takes place by cutting working of material, which in particular through the parameters of width and depth of cut partially permits a progressive, degressive or constant force level pattern. The force level and its pattern, though, are identical for all occupants.

It is an object of the invention to provide a belt retractor which allows a more flexible setting of the force level.

BRIEF SUMMARY OF THE INVENTION

The belt retractor according to the invention comprises a belt spool rotatably mounted in a frame, a disc adapted to be blocked against rotation on the frame, and a force-limiting arrangement with a cutting body which is adapted to be guided into a coupling position in which the cutting body couples the belt spool to the disc such that upon a relative rotation between the disc and the belt spool, the cutting body cuts material, the force-limiting arrangement having a guiding-in mechanism which guides the cutting body into the coupling position as a function of accident-related data. Coming into consideration as accident-related data are, in particular, body data of the vehicle occupant, seating position data or data which are representative of the severity of the accident. This data can be determined for example by sensors or in another manner, such as for example by determining the length of the belt webbing withdrawn or the angular acceleration or rotational speed of the belt spool before a blocking. The belt retractor according to the invention therefore allows a force limitation which can be better adapted to the respective circumstances. In particular, the weight and/or the height of the occupant can be taken into account to a sufficient extent for an optimized setting of the force limitation.

An advantageous development of the belt retractor according to the invention makes provision that the guiding-in mechanism has at least one oblique plane formed on the belt spool or on the disc, the cutting body being adapted to slide on the disc into the coupling position.

According to a first embodiment, the cutting body is an inertial body, or the cutting body is coupled to an inertial body, which on exceeding a particular angular acceleration or rotational speed and subsequent blocking of the belt spool is moved into the coupling position owing to its inertia or the centrifugal force acting on it. Thereby, it can be achieved that the additional force limitation caused by material cutting takes place only for occupants with a high body weight. In the case of an abrupt deceleration of the vehicle, shortly before the blocking of the belt spool, in the case of a heavy occupant a more rapid belt webbing withdrawal takes place than in the case of a light occupant, who shows a “slower” forward displacement. Only in the first case are the inertia forces onto the cutting body great enough for a guiding-in into the coupling position.

It is expedient to provide a locking mechanism which holds the cutting body in an initial position. Thereby it is ensured that the cutting body under normal circumstances is not unintentionally guided into the coupling position.

The locking mechanism can have a pre-stressing spring and/or a mechanical stop.

According to a second embodiment of the belt retractor according to the invention, the guiding-in mechanism is coupled to a switching mechanism of the belt retractor with which, on rotation of the belt spool, switching functions can be carried out. Such a switching mechanism is known per se and is based on a planetary gear or a control disc coupled to the belt spool via a reduction gear. The switching mechanism is used in particular for a so-called child safety function which is usually activated after a complete withdrawal of the belt webbing. It ensures that the fully withdrawn belt webbing in fact can be wound onto the belt spool again, but can no longer be withdrawn therefrom, in order to thus make possible a reliable fastening of a child's seat on a vehicle seat by means of a safety belt. The underlying mechanism, which provides for a switching process dependent on the length of the belt webbing withdrawn, can be made use of for the invention. Thus, after withdrawal of a particular belt webbing length, a switching process can be carried out, which leads to a guiding-in of the cutting body into the coupling position. As the length of belt webbing withdrawn is representative of the size of an occupant, therefore automatically a size-dependent setting of the force limitation level takes place.

A coupling of the guiding-in mechanism to the switching mechanism can take place in that the guiding-in mechanism has a guiding-in element, connected with the cutting body, which is movable by the switching mechanism.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a diagrammatic sectional view of a belt retractor with a force-limiting arrangement;

FIG. 2 shows a diagrammatic sectional view of a guiding-in mechanism of the force-limiting arrangement according to a first embodiment;

FIGS. 3, 4 show two variants of the guiding-in mechanism of FIG. 2;

FIG. 5 shows a diagrammatic sectional view of a guiding-in mechanism of the force-limiting arrangement according to a second embodiment;

FIG. 6 shows a variant of the guiding-in mechanism of FIG. 5;

FIG. 7 a shows a diagrammatic end face view of a guiding-in mechanism of the force-limiting arrangement according to a third embodiment;

FIG. 7 b shows a sectional view along the line B-B in FIG. 7 a; and

FIG. 8 shows a diagram of forces of the force-limiting arrangement according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The belt retractor shown diagrammatically in FIG. 1 has a frame 10 and a belt spool 12 rotatably mounted in the frame 10. A disc 16, which can rest against the frame 10 so as to be blocked against rotation by a blocking mechanism 18, is joined to a flange 14 of the belt spool 12. The disc 16 is connected for joint rotation with the flange 14 of the belt spool 12 up to a certain torque, for example by shear pins. In the hollow interior of the belt spool 12, a torsion rod 20 is arranged, which is coupled at one axial end for rotation with the disc 16, and at the opposite end for rotation with the belt spool 12. A cutting body 22 rests on the disc 16. The cutting body 22 can be raised by a guiding-in mechanism in the axial direction (in relation to the rotation axis of the belt spool 12 and the disc 16) from an initial position into a coupling position, in which it projects axially beyond the end face of the disc 16 facing the flange 14.

In FIG. 2 a first embodiment of the belt retractor is shown, in which the cutting body 22 rests inter alia on two oblique planes 24 formed in a depression of the end face of the disc 16. The cutting body 22, which is illustrated in FIG. 2 in an initial position, is held by a locking mechanism in the axial direction. The locking mechanism comprises here a mechanical stop in the form of an extension 26, formed integrally with the cutting body 22, which engages into an associated mounting 28 on the disc 16. In addition, the cutting body 22 is secured by a bolt 30 (or a screw) screwed into the cutting body 22, which penetrates the disc 16 in an oblong hole 32. A spring 36 arranged between the disc 16 and the head 34 of the bolt 30 braces the cutting body 22 towards the disc 16. Generally, one of the two measures is sufficient in order to hold the cutting body 22 in the initial position under normal circumstances.

In a case of blocking, triggered in a vehicle-sensitive or belt webbing-sensitive manner, the disc 16 is blocked by the blocking mechanism 18 against rotation on the frame 10 of the belt retractor. Thereby also the belt spool 12 is coupled non-rotatably to the frame 10 via the torsion rod 20, so that further rotation of the belt spool 12 in the belt webbing withdrawal direction A is prevented. On exceeding a predetermined belt load, however, the torsion rod 20 twists and permits a belt force limiting rotation of the belt spool 12 relative to the disc 16.

In addition to the known belt force limitation by the torsion rod 20, an additional force limitation can take place through a guiding in of the cutting body 22 into the coupling position. Whether or not such a guiding in takes place depends on the angular acceleration or the rotational speed of the belt spool 12 before its blocking. The belt webbing withdrawal taking place before the blocking of the belt spool 12 brings about a rotation of the belt spool 12, which is caused by the forward movement of the occupant in the case of an abrupt deceleration of the vehicle, the extent of the angular acceleration or the rotational speed depending in particular on the weight of the occupant.

The oblique planes 24 and the cutting body 22 are coordinated with each other such that on exceeding a particular rotational speed of the belt spool 12 in the belt webbing withdrawal direction and subsequent blocking of the belt spool 12, the cutting body 22, owing to its mass moment of inertia, overcomes the static friction and the pre-stressing force of the spring 36 and slides on the oblique planes 24 into the coupling position. With this movement of the cutting body 22, the extension 26 comes out of engagement with the mounting 28, and the bolt 30 is displaced in the oblong hole 32 until the cutting body 22 comes to lie on the elevated support surfaces 38. A cutting edge 40 of the cutting body 22 projects in this elevated position into a recess 42 in the flange 14 of the belt spool 12. Upon a rotation of the belt spool 12 relative to the disc 16 in the belt webbing withdrawal direction, accompanied by twisting of the torsion rod 20, the cutting edge 40 of the cutting body 22 comes into engagement with the material of the flange 14, a shoulder 44 of the recess 42 pressing the cutting body 22 against a stop 46 of the disc 16. The bolt 30 is dimensioned such that with this thrust movement it is sheared off. The sheared off part of the bolt 30 is pushed into a free space in which previously a part of the cutting body 22 was received. A further relative rotation between the belt spool 12 and the disc 16 is now only possible by the cutting edge 40 of the cutting body 22 cutting a chip out of the flange 14.

Therefore, an energy conversion takes place through material cutting, which is effected parallel to the energy conversion through the twisting of the torsion rod 20. The profile of the force level of the additional limitation as a function of the rotation angle of the belt spool 12 is determined substantially by the width and depth of cut.

In FIGS. 3 and 4 two variants of the guiding-in mechanism are shown, in which the cutting body 22 is held by an inertia spring 48 and respectively 50 arranged between the flange 14 of the belt spool 12 and the cutting body 22 and respectively between the stop 46 of the disc 16 and the cutting body 22.

Whereas in the first embodiment shown in FIGS. 2 to 4 the guiding-in mechanism is formed substantially solely by the oblique planes 24, in the second, similarly constructed embodiment shown in FIGS. 5 and 6, the guiding-in of the cutting body 22 takes place by means of a switching element 52 (only illustrated symbolically). The switching element 52 is part of a switching mechanism known per se, with which switching functions can be carried out on rotation of the belt spool 12. The switching mechanism is designed so that the switching element 52 carries out a switching movement after withdrawal of a particular length of belt webbing from the belt spool 12. In so doing, the switching element 52 engages the bolt 30 such that the latter raises the cutting body 22 into the coupling position. In this embodiment, the bolt 30 therefore serves as guiding-in element, but just as in the first embodiment is sheared off by the thrust movement of the flange 14 of the belt spool 12.

In contrast to the first embodiment, in this embodiment a guiding-in of the cutting body 22 does not take place as a function of the angular acceleration or the rotational speed of the belt spool 12 before its blocking, but rather as a function of the length of the belt webbing withdrawn or the belt webbing remaining on the belt spool 12, which depends substantially on the size of the occupant.

FIG. 6 shows a variant of the second embodiment. Here, the pre-stressing spring 36 is arranged between the disc 16 and the cutting body 22, so that the cutting body 22 is pre-stressed into the coupling position, but is held in the initial position by the switching element 52. By an actuation of the switching element 52, the cutting body 22 is guided from the initial position into the coupling position shown in FIG. 6.

FIGS. 7 a and 7 b illustrate a third embodiment the guiding-in mechanism of which is constructed similarly to that of the first embodiment. Here, the cutting body 22 is guided into the coupling position as a function of the centrifugal force F_(Z) acting on the cutting body 22. Depending on the physical constitution of the vehicle occupant, in fact a significant difference in the speed of belt webbing withdrawal and hence in the rotational speed of the belt spool 12 or the disc 16 can be seen during belt webbing withdrawal. The mechanical implementation of the guiding-in mechanism of this embodiment proceeds from the finding that this speed can only differ when a resistance has arisen at the belt webbing, because it is not until then that the specific kinetic energy of the occupant also has an influence (E=½ mv²).

Accordingly, provision is made that initially a force limitation takes place on a basic level by means of the torsion rod 20 only. (This level could be designed, for example, as a predefined ideal level for a so-called 5% occupant.) But if the rotational speed of the belt spool 12 exceeds a specific limiting value, the cutting body 22 is additionally connected owing to the higher centrifugal force F_(Z), so that the level of force limitation is raised. (This level may be designed as a predefined ideal level for 50% or 95% occupants.) If, on the other hand, the rotational speed of the belt spool 12 remains below the predefined limiting value, the switching process does not occur and the force limitation is effected at the lower level.

FIG. 8 shows the different levels of force limitation in a diagram in which the force limitation is illustrated as a function of the belt webbing withdrawal.

In all embodiments, the guiding-in of the cutting body 22 into the coupling position can also take place by means of a control element which is coupled to the cutting body 22 and is moved as a function of the angular acceleration/rotational speed of the belt spool or the belt webbing withdrawal length.

The pre-stressing springs 36, 48, 50 of the different embodiments/variants can be designed such that they serve not only for securing the cutting body or a control element, but also for setting the inertia, i.e. the necessary angular acceleration of the belt spool for a guiding-in of the cutting body into the coupling position, and hence the moment of guiding in. The pre-stressing springs can be formed in particular by the usual inertia springs in belt retractors.

It is also possible to combine features of different embodiments with each other. In addition, the cutting body 22 can, as an alternative, be arranged on the belt spool 12 and cut material on the disc 16. 

1. A belt retractor, comprising a belt spool rotatably mounted in a frame, a disc adapted to be blocked against rotation on the frame, and a force-limiting arrangement with a cutting body which is adapted to be guided into a coupling position in which the cutting body couples the belt spool to the disc such that upon a relative rotation between the disc and the belt spool, the cutting body cuts material, the force-limiting arrangement having a guiding-in mechanism which guides the cutting body into the coupling position as a function of accident-related data.
 2. The belt retractor according to claim 1, wherein the guiding-in mechanism has at least one oblique plane formed on the belt spool or on the disc, the cutting body being adapted to slide on the disc into the coupling position.
 3. The belt retractor according to claim 1, wherein the cutting body is an inertial body which on exceeding a particular angular acceleration or rotational speed and subsequent blocking of the belt spool is moved into the coupling position owing to one of the inertia of the inertial body, and the centrifugal force F_(Z) acting on the inertial body.
 4. The belt retractor according to claim 1, wherein the cutting body is coupled to a control element in the form of an inertial body which on exceeding a particular angular acceleration or rotational speed and subsequent blocking of the belt spool is moved into the coupling position owing to one of: the inertia of the inertial body, and the centrifugal force F_(Z) acting on the inertial body.
 5. The belt retractor according to claim 1, further including a locking mechanism which holds the cutting body in an initial position.
 6. The belt retractor according to claim 5, wherein the locking mechanism has a pre-stressing spring.
 7. The belt retractor according to claim 5, wherein the locking mechanism has a mechanical stop.
 8. The belt retractor according to claim 1, wherein the guiding-in mechanism is coupled to a switching mechanism of the belt retractor with which, on rotation of the belt spool, switching functions can be carried out.
 9. The belt retractor according to claim 8, wherein the guiding-in mechanism has a guiding-in element, connected with the cutting body, which is movable by the switching mechanism. 